The present invention relates to concrete transit mixing trucks. In particular, the invention relates to a control system for controlling rotation of the drum of the mixer truck while the truck is in motion.
Concrete transit mixer trucks are used to transport concrete to a worksite while mixing or agitating the payload of cement, aggregate, sand and water. Fins within the drum mix the payload as the drum rotates.
As the concrete constituents are initially loaded into the drum, and as the truck moves to the worksite, the drum is rotated in a first or charge direction, so that the payload tends to move away from discharge opening of the drum. At the worksite, the rotation of the drum is reversed so that it rotates in a second or discharge direction. The fins move the payload toward the discharge opening. A chute attached below the discharge opening delivers the concrete from the drum to the worksite.
The drum is rotated by a hydraulic drive. A hydraulic motor in the hydraulic drive is driven by the truck engine through a power takeoff connection. As a result, the speed of the hydraulic motor driving the drum will vary with engine speed.
The constantly moving concrete within the drum contacts the interior of the drum and fins. Over time, the fins and the interior lining of the drum will be worn to an extent that they require replacement. The replacement of the drum and the fins is an expensive repair.
On average, the drum and fins of a concrete transit mixer truck will require replacement about every 1.5 million revolutions of the drum. Thus, the faster the drum is rotated on average, the sooner the drum and fins will require replacement.
Some concrete transit mixer trucks have been provided with a constant drum speed feature, in which the hydraulic motor is operated at a constant speed, rather than at a variable speed that is a function of the truck engine speed. By using the constant drum speed feature while the truck is traveling to the worksite, the constant rotational speed of the drum will generally be less than the average rotational speed of the drum if the hydraulic motor were allowed to vary with engine speed. A 30 to 40 percent reduction in the number of revolutions can be achieved if constant drum speed is used whenever the truck is traveling to or from a worksite. This can yield significant benefits in maintenance costs for the truck. In addition, it can result in significant savings in fuel and a gain in effective horsepower, because the drum is not accelerated whenever the engine accelerates.
Despite the benefits of a constant drum speed feature, it has not achieved widespread usage, even among businesses owning the trucks with the constant drum speed feature. Because the driver must turn on the constant drum speed feature when traveling, the use of the constant speed feature is dependent upon the driver remembering to activate the system. In addition, many drivers believe that they can control the truck and the drum better themselves manually, and therefore choose not to use the constant speed feature.